Method for manufacturing silicon single crystal

ABSTRACT

There is provided a method for manufacturing a silicon single crystal, the method includes: a raw material melting step of melting polycrystalline silicon accommodated in a crucible to obtain a silicon melt; and bringing a seed crystal into contact with the silicon melt and pulling up the seed crystal to grow the silicon single crystal, wherein, after the raw material melting step and before the pulling step, there are performed: a cristobalitizing step of leaving the silicon melt at a predetermined number of rotations of the crucible with a predetermined gas flow rate and a predetermined furnace pressure to generate cristobalite while applying a magnetic field; and a dissolving step of partially dissolving the cristobalite by carrying out any one of an increase in number of rotations of the crucible, an increase in gas flow rate, and a reduction in furnace pressure beyond counterpart figures in the cristobalitizing step.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a siliconsingle crystal based on the Czochralski method.

BACKGROUND ART

The Czochralski method has been conventionally widely adopted for growthof a silicon single crystal. Among others, the MCZ method (the magneticfield applied Czochralski method) for applying a magnetic field to asilicon melt in order to suppress a convection current of a silicon meltin a quartz crucible has been known. In the MCZ method, a silicon singlecrystal is grown by performing a melting step of accommodatingpolycrystalline silicon in a quartz crucible and melting thepolycrystalline silicon in the quartz crucible with use of a heater anda pulling step of bringing a seed crystal into contact with a meltsurface of the silicon melt from above, rotating and moving up and downthe seed crystal and the quartz crystal while applying a magnetic fieldto the silicon melt with use of a coil, and pulling the seed crystal.

The quartz crucible configured to accommodate the silicon melt thereinis made of amorphous SiO₂ (quartz glass) having an amorphous structure.The quartz crucible reacts with the silicon melt, and a cristobalitecrystal layer, which is crystalline SiO₂, is formed on a SiO₂/Siinterface, i.e., an inner surface of the quartz crucible that is incontact with the silicon melt. In some cases, the cristobalite crystallayer is exfoliated during pulling up the silicon single crystal,liberated or allowed to fall into the silicon melt from the quartzcrucible, and reaches a growth interface of a silicon single crystalthat is being pulled up. As a result, the cristobalite crystal layerenters the silicon single crystal that is being pulled up, and it maycause dislocation generation of the silicon single crystal.

Thus, to prevent exfoliation of cristobalite from the inner surface ofthe quartz crucible during the silicon single crystal pulling step andavoid the dislocation generation of the silicon single crystal, variousmethods have been suggested. For example, Patent Literature 1 disclosesa method for growing a silicon single crystal while applying a magneticfield to a silicon melt with use of a quartz crucible having an aluminumlow concentration layer on an inner surface side.

However, according to the method disclosed in Patent Literature 1, aproblem lies in that the aluminum low concentration layer (an impuritylayer) is formed in the quartz crucible and hence this impurity iscontained in the silicon single crystal. If the impurity is contained inthe silicon single crystal, an influence on a device is a concern, andhence forming the impurity layer on an inner surface of the quartzcrucible is not preferable. Especially, this is particularly undesirablesolving means for a next-generation device that is expected to achievehigh purity.

Further, Patent Literature 2 discloses intermittently applying amagnetic field to a silicon melt to control a size of cristobalite.However, to intermittently apply a magnetic field to the silicon meltmore than once, magnetization and demagnetization of a coil must berepeated, this operation is troublesome, and a risk of operationalerrors is increased. Furthermore, when the magnetization and thedemagnetization of the coil are repeated, a dead time that the siliconsingle crystal is not manufactured is increased, which is inefficient.

CITATION LIST Patent Literatures

Patent Literature 1: Japanese Unexamined Patent Application PublicationNo. 2010-30816

Patent Literature 2: Japanese Unexamined Patent Application PublicationNo. 2001-240494

Patent Literature 3: Japanese Unexamined Patent Application PublicationNo. H10-297994

SUMMARY OF INVENTION Technical Problem

In view of the above-described problem, it is an object of the presentinvention to provide a silicon single crystal manufacturing method thatsuppresses generation of a dislocation at the time of manufacturing thesilicon single crystal.

Solution to Problem

To achieve the object, according to the present invention, there isprovided a method for manufacturing a silicon single crystal, the methodcomprising: a raw material melting step of melting polycrystallinesilicon accommodated in a crucible to obtain a silicon melt; and apulling step of bringing a seed crystal into contact with a melt surfaceof the silicon melt and pulling up the seed crystal to grow the siliconsingle crystal, wherein, after the raw material melting step and beforethe pulling step, there are performed: a cristobalitizing step ofleaving the silicon melt at a predetermined number of rotations of thecrucible with a predetermined gas flow rate and a predetermined furnacepressure to generate cristobalite on a surface of the crucible whileapplying a magnetic field; and a dissolving step of partially dissolvingthe cristobalite by carrying out any one of an increase in number ofrotations of the crucible, an increase in gas flow rate, and a reductionin furnace pressure beyond counterpart figures in the cristobalitizingstep.

According to such a method for manufacturing a silicon single crystal,when the surface of the crucible on which cristobalite was oncegenerated is daringly appropriately dissolved and an ideal surface stateof the crucible is produced, the silicon single crystal manufacturingmethod that suppresses generation of a dislocation is provided.

Moreover, the same magnetic field as that in the cristobalitizing stepcan be applied at the dissolving step.

As described above, cristobalite can be partially dissolved by justperforming, e.g., an increase in the number of rotations of the cruciblewhile keeping the cristobalitizing step and the application of themagnetic field, and hence a dead time that the silicon single crystal isnot manufactured can be shortened.

Additionally, at the cristobalitizing step, it is preferable to adjustthe number of rotations of the crucible to 3 rpm or less, adjust the gasflow rate to 250 L/min or less, and adjust the furnace pressure to 80hPa or more.

When the adjustment is carried out in this manner, the cristobalite isappropriately produced, and dislocation generation can be furthereffectively avoided.

Further, it is preferable to perform the cristobalitizing step for onehour or more.

When such a time period is provided, it is a time that is sufficient toform the cristobalite on the surface of the crucible, and it is also asufficiently short time in terms of efficiency.

Furthermore, at the dissolving step, it is preferable to increase thenumber of rotations of the crucible to 5 rpm or more, increase the gasflow rate to 300 L/min or more, and reduce the furnace pressure to 70hPa or less.

When the adjustment is carried out in this manner, the cristobalite isappropriately dissolved, and the dislocation generation can be furthereffectively avoided.

Moreover, it is preferable to perform the dissolving step for one houror more and nine hours or less.

As described above, when the time of the dissolving step is one hour ormore, dissolution can be sufficiently carried out to the extent that thecristobalite is not exfoliated and, even if the cristobalite isexfoliated, the exfoliated cristobalite becomes sufficiently thin to bedissolved in the silicon melt before it reaches a solid-liquidinterface. Additionally, when the time of the dissolving step is ninehours or less, it is possible to prevent the generated cristobalite frombeing entirely dissolved and also prevent new nucleation of thecristobalite from occurring.

Further, it is preferable to use a horizontal magnetic field as themagnetic field to be applied and set intensity of a center magneticfield thereof to 3000 gausses or more and 5000 gausses or less at thecristobalitizing step, the dissolving step, or both the cristobalitizingstep and the dissolving step.

As described above, when the horizontal magnetic field is applied andintensity of its center magnetic field is 3000 gausses or more, aleaving time can be shortened, which is efficient. On the other hand,application of 5000 gausses is sufficient.

Advantageous Effects of Invention

As described above, according to the method for manufacturing a siliconsingle crystal of the present invention, when the crucible surface onwhich cristobalite was once generated is daringly appropriatelydissolved and the ideal crucible surface state is formed, generation ofa dislocation in growth of the silicon single crystal can be suppressed.Furthermore, when an increase in number of rotations of the crucible orthe like is performed without changing application of the magneticfield, the cristobalite can be partially dissolved, and hence the deadtime that the silicon single crystal is not manufactured can beshortened.

DESCRIPTION OF EMBODIMENTS

An embodiment according to the present invention will now be describedhereinafter, but the present invention is not restricted thereto.

As disclosed in Patent Literature 2 or Patent Literature 3, thecristobalite is formed on the surface of the crucible in an environmentwhere the magnetic field is applied to the silicon melt, and the formedcristobalite is gradually dissolved in the silicon melt in anenvironment where the application of the magnetic field is stopped. Inconventional examples, a problem lies in that this cristobalite isexfoliated into the silicon melt, resulting in the dislocationgeneration of the silicon single crystal that is in the growth process.

The present inventors applied a magnetic field of 4000 gausses to asilicon melt after end of a polycrystalline silicon melting step, leftthe silicon melt for one hour, then pulled a silicon single crystalbased on the MCZ method, observed cristobalite formed on a surface of acrucible, and consequently found traces of exfoliation of thecristobalite near the center of a so-called a brown ring. On the otherhand, after end of the polycrystalline silicon melting step, the presentinventors applied a magnetic field of 4000 gausses to the silicon melt,left the silicon melt for one hour, then performed any one of anincrease in the number of rotations of the crucible, an increase in gasflow rate, and a reduction in furnace pressure, and pulled the crystalbased on the MCZ method, but the brown ring was not observed on thesurface of the crucible since it was dissolved, a majority of the brownring turned into amorphous silica, and dappled cristobalite was formedtherein in an island-like pattern.

The number of times that dislocation generation occurs was checked withrespect to 10 pieces of silicon single crystal grown based on the MCZmethod immediately after applying the magnetic field and leaving themelt and 10 pieces of silicon single crystal grown based on the MCZmethod after applying the magnetic field, leaving the melt, and thenperforming, e.g., an increase in number of rotations of the crucible,respectively. As a result, the dislocation generation occurred in all ofthe 10 pieces of silicon single crystal when just the magnetic field wasapplied and the melt was left, whereas the dislocation generation wasnot observed when the increase in number of rotations of the cruciblewas further performed after these processes.

As a result, it was understood that, when just the magnetic field isapplied to the silicon melt and the silicon melt is left, the formedcristobalite is exfoliated during the pulling step and the exfoliatedcristobalite reaches the solid-liquid interface during the siliconsingle crystal growth before it is completely dissolved into the siliconmelt, thus leading to the dislocation generation of the silicon singlecrystal. On the other hand, it was revealed that, when the cristobaliteis appropriately dissolved by performing, e.g., the increase in numberof rotations of the crucible, the exfoliation of the cristobalite can besuppressed, and the dislocation generation of the silicon single crystaldoes not occur. Further, even if the cristobalite is exfoliated from thecrucible, since a thickness of the appropriately dissolved cristobaliteis small, the cristobalite is dissolved in the silicon melt withoutreaching the solid-liquid interface of the silicon single crystal, andthe dislocation generation of the silicon single crystal during thegrowth does not occur.

On the surface of the crucible obtained by applying the magnetic field,leaving the silicon melt, performing, e.g., an increase in number ofrotations of the crucible for a long time, completely dissolving thecristobalite, and then pulling the silicon single crystal, the brownring was again observed, and traces of exfoliation of the cristobalitewere observed near the center of the brown ring. This means that theentire surface of the crucible returns to a state close to initialamorphous silica when the cristobalite is completely dissolved, andnucleation, growth, and exfoliation of the cristobalite again occur atthe time of the pulling step. That is, it suggests that new nucleationof the cristobalite hardly occurs when the cristobalite remains on thesurface of the crucible, but the nucleation can occur when the entiresurface is in the amorphous silica state. Thus, it was found out that,when all of the cristobalite is dissolved, the dislocation generation ofthe silicon single crystal possibly occurs at the time of the subsequentpulling step.

Therefore, based on the above knowledge, the present inventors conceiveda view that the dislocation generation of the silicon single crystalthat is in the growth process is suppressed when the surface state ofthe crucible before the crystal pulling step is a state that a largepart of the surface of the crucible is constituted of amorphous silicaand the dappled cristobalite is formed in the amorphous silica in anisland-like pattern. Furthermore, they discovered that the ideal surfacestate of the crucible that the cristobalite is not exfoliated and newnucleation of the cristobalite does not occur can be formed by applyinga magnetic field to the silicon melt, leaving the silicon melt, formingthe cristobalite on the surface of the crucible, and then performing,e.g., an increase in number of rotations of the crucible toappropriately dissolve the cristobalite. Moreover, since control over,e.g., the number of rotations of the crucible can be instantaneouslyperformed, they revealed that time loss does not occur as compared witha case where the application of the magnetic field is controlled, and aburden on an operator can be reduced. Therefore, the present inventorsdiscovered the silicon single crystal manufacturing method that enablesavoiding the dislocation generation of the silicon single crystal andhit upon the present invention. Particulars of the present inventionwill now be described hereinafter.

A raw material melting step according to the present invention is a stepof melting polycrystalline silicon accommodated in the crucible andobtaining a silicon melt. Conditions for this step can be set inaccordance with an amount of the polycrystalline silicon to be molten,and this step can be carried out based on a generally effected methodfor melting the polycrystalline silicon.

A cristobalitizing step according to the present invention is a step forleaving the silicon melt at a predetermined number of rotations of thecrucible with a predetermined gas flow rate and a predetermined furnacepressure and producing cristobalite on a surface of the crucible whileapplying a magnetic field after the raw material melting step. Based onthis step, the crucible reacts with the silicon melt, and thecristobalite is formed on an interface of the crucible and the siliconmelt.

As leaving conditions in this case, it is preferable to adjust thenumber of rotations of the crucible to 3 rpm or less, adjust the gasflow rate to 250 L/min or less, and adjust the furnace pressure to 80hPa or more. When such adjustment is carried out, the cristobalite isappropriately produced, and the dislocation generation can be furtheravoided. Additionally, to uniformly heat the crucible, the number ofrotations of the crucible is preferably 0.1 rpm or more. Further, toprevent an oxide from adhering to an in-furnace component, the gas flowrate is preferably 100 L/min or more. Furthermore, to perform adepressurizing operation, the furnace pressure is preferably 300 hPa orless.

Moreover, it is preferable to carry out the cristobalitizing step forone hour or more. If the time for applying a magnetic field and leavingthe silicon melt is one hour or more, it is a time that is sufficient toform the cristobalite on the surface of the crucible, and it is also atime that is sufficiently short in terms of efficiency withoutunnecessarily increasing a dead time that the silicon single crystal isnot grown. Additionally, it is preferable to set a maximum time forleaving the silicon melt after the application of the magnetic field to10 hours. If the time for leaving the silicon melt after the applicationof the magnetic field is 10 hours or less, it is possible to avoid asituation that formation of the cristobalite on the surface of thecrucible advances too much and sufficient dissolution cannot beperformed at the subsequent dissolving step.

Further, it is preferable to adopt a horizontal magnetic field as themagnetic field applied in this case and set the intensity of the centermagnetic field to 3000 gausses or more and 5000 gausses or less. If theintensity of the center magnetic field is 3000 gausses or more, theleaving time can be reduced, which is industrially efficient. On theother hand, application of 5000 gausses or more is sufficient.

The dissolving step according the present invention is a step ofpartially dissolving the cristobalite by performing any one of anincrease in number of rotations of the crucible, an increase in gas flowrate, and a reduction in furnace pressure beyond counterpart figures inthe cristobalitizing step after the cristobalitizing step. Since thecristobalite is partially dissolved by a simple method, e.g., theincrease in number of rotations of the crucible as described above, itis possible to avoid a case where a burden on an operator is raised ormistakes are increased at other complicated steps and time loss therebyoccurs. This step enables appropriately dissolving the cristobaliteformed on the surface of the crucible and suppressing the exfoliationduring the pulling step, and hence the dislocation generation arisingfrom the cristobalite can be prevented.

It is to be noted that the cristobalite is prevented from being entirelydissolved at this step. When the cristobalite is fully dissolved and theentire surface of the crucible becomes close to a state of initialamorphous silica, nucleation of the cristobalite is apt to newly occurif the magnetic field was applied at the pulling step, and there is apossibility that the newly produced cristobalite is exfoliated duringthe pulling step and the dislocation generation occurs.

Furthermore, at the dissolving step, it is preferable to apply the samemagnetic field as that used in the cristobalitizing step. When the samemagnetic field is applied in this manner, magnetization ordemagnetization of the magnetic field, intensity control, and others donot have to be performed, and a dead time that the silicon singlecrystal is not manufactured can be shortened. In addition, it ispreferable that intensity of the magnetic field applied at this time isthe same as that in the cristobalitizing step, and it is preferable toadopt a horizontal magnetic field as the magnetic field to be appliedand set intensity of a center magnetic field to 3000 gausses or more and5000 gausses or less. Such a range is industrially efficient.

In this step, it is preferable to increase the number of rotations ofthe crucible to 5 rpm or more, preferable to increase the gas flow rateto 300 L/min or more, and preferable to reduce the furnace pressure to70 hPa or less. When such adjustment is carried out, the cristobalitecan be appropriately dissolved, and the dislocation generation can befurther avoided. Additionally, when the number of rotations is too high,progress of dissolution is too fast, appropriate control over thedissolution is difficult, and hence 20 rpm or less is desirable as thenumber of rotations of the crucible. Further, when the flow rate is toohigh, the progress of the dissolution is too fast, the appropriatecontrol over the dissolution becomes difficult, the flow rate does nothave to be increased in view of economy, and hence 500 L/min or less issufficient as the gas flow rate. Furthermore, when the depressurizationis excessively performed, the progress of the dissolution is too fast,the appropriate control over the dissolution becomes difficult, andhence 10 hPa or more is preferable as the furnace pressure.

Moreover, the time of the dissolving step is preferably one hour or moreand nine hours or less. If the time of the dissolving step is one houror more, the dissolution can be sufficiently carried out so that thecristobalite cannot be exfoliated and, even if the cristobalite isexfoliated, the exfoliated cristobalite is sufficiently thin to bedissolved in the silicon melt before reaching the solid-liquidinterface. Additionally, if the time of the dissolving step is ninehours or less, it is possible to avoid a situation where all of thecristobalite is dissolved and new nucleation of the cristobalite occurs.

The pulling step according to the present invention is a step ofbringing a seed crystal into contact with a melt surface of the siliconmelt after the melting step and pulling it upward to grow the siliconsingle crystal. This step can be performed by setting conditions inaccordance with specifications of the silicon single crystal to bepulled and by using a generally adopted silicon single crystal pullingmethod.

EXAMPLES

The present invention will now be described in more details hereinafterwith reference to examples and comparative examples, but the presentinvention is not restricted to the following examples.

Examples 1-1 to 1-13, and Comparative Example 1

Polycrystalline silicon accommodated in a crucible was molten to obtaina silicon melt, the silicon melt was left at the number of rotations(rpm) of the crucible, a gas flow rate (L/min), and a furnace pressure(hPa) shown in Table 1 while applying a horizontal magnetic field havingcenter magnetic field intensity of 4000 gausses, and cristobalite wasproduced on a surface of the crucible (a cristobalitizing step). Then,the number of rotations of the crucible was increased as shown in Table1 without changing the gas flow rate and the furnace pressure and thecristobalite was partially dissolved while applying the same horizontalmagnetic field except Comparative Example 1 (a dissolving step). Atlast, a seed crystal was brought into contact with a melt surface of thesilicon melt and pulled upward, thereby growing a silicon single crystalhaving a diameter of 300 mm. Table 1 shows the number of times ofdislocation generation when 10 pieces of silicon single crystal werepulled under respective conditions.

TABLE 1 Cristobalitizing step Dissolving step Number Number Intensity ofNumber Intensity of of times of rota- Flow Pres- magnetic of rota- FlowPres- magnetic of tions rate sure field Time tions rate sure field Timedislocation (rpm) (L/min) (hPa) (Gauss) (h) (rpm) (L/min) (hPa) (Gauss)(h) generation Example 1 200 100 4000 5 6 200 100 4000 5 0 1-1 Example 3200 100 4000 5 6 200 100 4000 5 0 1-2 Example 5 200 100 4000 5 6 200 1004000 5 6 1-3 Example 1 200 100 4000 0.5 6 200 100 4000 5 7 1-4 Example 1200 100 4000 1 6 200 100 4000 5 0 1-5 Example 1 200 100 4000 8 6 200 1004000 5 0 1-6 Example 1 200 100 4000 10 6 200 100 4000 5 2 1-7 Example 1200 100 4000 5 3 200 100 4000 5 7 1-8 Example 1 200 100 4000 5 5 200 1004000 5 0 1-9 Example 1 200 100 4000 5 6 200 100 4000 0.5 6 1-10 Example1 200 100 4000 5 6 200 100 4000 1 0 1-11 Example 1 200 100 4000 5 6 200100 4000 7 0 1-12 Example 1 200 100 4000 5 6 200 100 4000 9 3 1-13Comparative 3 200 100 4000 10 N/A 10 Example 1

In Comparative Example 1 where the cristobalitizing step alone isperformed, the 10 pieces of silicon single crystal were all underwentthe dislocation generation. It can be considered this dislocationgeneration occurred because the cristobalite was exfoliated to cause thedislocation generation since the dissolving step was not carried out. Onthe other hand, in Examples 1-1 to 1-13, the number of times ofdislocation generation was successfully reduced. In particular, Examples1-1 to 1-3 showed that the number of rotations of the crucible in thecristobalitizing step was preferably 3 rpm or less, and Examples 1-4 to1-7 showed that the time of the cristobalitizing step was preferably onehour or more and 10 hours or less. Furthermore, Examples 1-8 to 1-9showed that the number of rotations of the crucible in the dissolvingstep was preferably 5 rpm or more, and Examples 1-10 to 1-13 showed thatthe time of the dissolving step was preferably one hour or more and ninehours or less.

In particular, based on the above results, it is preferable to leave thesilicon melt at the number of rotations that is 3 rpm or less for onehour or more to carry out the cristobalitizing step and then perform thedissolving step at the number of rotations that is 5 rpm or more for onehour or more and nine hours or less.

Examples 2-1 to 2-14, and Comparative Example 2

Polycrystalline silicon accommodated in a crucible was molten to obtaina silicon melt, the silicon melt was left at the number of rotations(rpm) of the crucible, a gas flow rate (L/min), and a furnace pressure(hPa) shown in Table 2 while applying a horizontal magnetic field havingcenter magnetic field intensity of 4000 gausses, and cristobalite wasproduced on a surface of the crucible (a cristobalitizing step). Then,the gas flow rate was increased as shown in Table 2 without changing thenumber of rotations of the crucible and the furnace pressure, and thecristobalite was partially dissolved while applying the same horizontalmagnetic field except Comparative Example 2 (a dissolving step). Atlast, a seed crystal was brought into contact with a melt surface of thesilicon melt and pulled upward, thereby growing a silicon single crystalhaving a diameter of 300 mm. Table 2 shows the number of times ofdislocation generation when 10 pieces of silicon single crystal werepulled under respective conditions.

TABLE 2 Cristobalitizing step Dissolving step Number Number Intensity ofNumber Intensity of of times of rota- Flow Pres- magnetic of rota- FlowPres- magnetic of tions rate sure field Time tions rate sure field Timedislocation (rpm) (L/min) (hPa) (Gauss) (h) (rpm) (L/min) (hPa) (Gauss)(h) generation Example 1 220 100 4000 3 1 330 100 4000 5 0 2-1 Example 1250 100 4000 3 1 330 100 4000 5 0 2-2 Example 1 280 100 4000 3 1 330 1004000 5 7 2-3 Example 1 220 100 4000 0.5 1 330 100 4000 5 6 2-4 Example 1220 100 4000 1 1 330 100 4000 5 0 2-5 Example 1 220 100 4000 5 1 330 1004000 5 0 2-6 Example 1 220 100 4000 8 1 330 100 4000 5 0 2-7 Example 1220 100 4000 10 1 330 100 4000 5 2 2-8 Example 1 220 100 4000 3 1 270100 4000 5 7 2-9 Example 1 220 100 4000 3 1 300 100 4000 5 0 2-10Example 1 220 100 4000 3 1 330 100 4000 0.5 6 2-11 Example 1 220 1004000 3 1 330 100 4000 1 0 2-12 Example 1 220 100 4000 3 1 330 100 4000 70 2-13 Example 1 220 100 4000 3 1 330 100 4000 9 3 2-14 Comparative 1220 100 4000 6 N/A 10 Example 2

In Comparative Example 2 where the cristobalitizing step alone isperformed, the 10 pieces of silicon single crystal were all underwentthe dislocation generation. It can be considered this dislocationgeneration occurred because the cristobalite was exfoliated to cause thedislocation generation since the dissolving step was not carried out. Onthe other hand, in Examples 2-1 to 2-14, the number of times ofdislocation generation was successfully reduced. In particular, Examples2-1 to 2-3 showed that the gas flow rate in the cristobalitizing stepwas preferably 250 L/min or less, and Examples 2-4 to 2-8 showed thatthe time of the cristobalitizing step was preferably one hour or moreand 10 hours or less. Furthermore, Examples 2-9 to 2-10 showed that thegas flow rate in the dissolving step was preferably 300 L/min or more,and Examples 2-11 to 2-14 showed that the time of the dissolving stepwas preferably one hour or more and nine hours or less.

In particular, based on the above results, it is preferable to leave thesilicon melt with the flow rate of 250 L/min or less for one hour ormore to carry out the cristobalitizing step and then perform thedissolving step with the flow rate of 300 L/min or more for one hour ormore and nine hours or less.

Examples 3-1 to 3-15, and Comparative Example 3

Polycrystalline silicon accommodated in a crucible was molten to obtaina silicon melt, the silicon melt was left at the number of rotations(rpm) of the crucible, a gas flow rate (L/min), and a furnace pressure(hPa) shown in Table 3 while applying a horizontal magnetic field havingcenter magnetic field intensity of 4000 gausses, and cristobalite wasproduced on a surface of the crucible (a cristobalitizing step). Then,the furnace pressure was reduced as shown in Table 3 without changingthe number of rotations of the crucible and the gas flow rate, and thecristobalite was partially dissolved while applying the same horizontalmagnetic field except Comparative Example 3 (a dissolving step). Atlast, a seed crystal was brought into contact with a melt surface of thesilicon melt and pulled upward, thereby growing a silicon single crystalhaving a diameter of 300 mm. Table 3 shows the number of times ofdislocation generation when 10 pieces of silicon single crystal werepulled under respective conditions.

TABLE 3 Cristobalitizing step Dissolving step Number Number Intensity ofNumber Intensity of of times of rota- Flow Pres- magnetic of rota- FlowPres- magnetic of tions rate sure field Time tions rate sure field Timedislocation (rpm) (L/min) (hPa) (Gauss) (h) (rpm) (L/min) (hPa) (Gauss)(h) generation Example 1 200 60 4000 3 1 200 50 4000 5 7 3-1 Example 1200 80 4000 3 1 200 50 4000 5 0 3-2 Example 1 200 100 4000 3 1 200 504000 5 0 3-3 Example 1 200 100 4000 0.5 1 200 50 4000 5 6 3-4 Example 1200 100 4000 1 1 200 50 4000 5 0 3-5 Example 1 220 100 4000 5 1 200 504000 5 0 3-6 Example 1 200 100 4000 8 1 200 50 4000 5 0 3-7 Example 1200 100 4000 10 1 200 50 4000 5 3 3-8 Example 1 200 100 4000 5 1 200 504000 5 0 3-9 Example 1 200 100 4000 5 1 200 70 4000 5 0 3-10 Example 1200 100 4000 5 1 200 90 4000 5 7 3-11 Example 1 200 100 4000 5 1 200 504000 0.5 7 3-12 Example 1 200 100 4000 5 1 200 50 4000 1 0 3-13 Example1 200 100 4000 5 1 200 50 4000 7 0 3-14 Example 1 200 100 4000 5 1 20050 4000 9 2 3-15 Comparative 1 200 100 4000 6 N/A 10 Example 3

In Comparative Example 3 where the cristobalitizing step alone isperformed, the 10 pieces of silicon single crystal were all underwentthe dislocation generation. It can be considered this dislocationgeneration occurred because the cristobalite was exfoliated to cause thedislocation generation since the dissolving step was not carried out. Onthe other hand, in Examples 3-1 to 3-15, the number of times ofdislocation generation was successfully reduced. In particular, Examples3-1 to 3-3 showed that the furnace pressure in the cristobalitizing stepwas preferably 80 hPa or more, and Examples 3-4 to 3-8 showed that thetime of the cristobalitizing step was preferably one hour or more and 10hours or less. Furthermore, Examples 3-9 to 3-11 showed that the furnacepressure in the dissolving step was preferably 70 hPa or less, andExamples 3-12 to 3-15 showed that the time of the dissolving step waspreferably one hour or more and nine hours or less.

In particular, based on the above results, it is preferable to leave thesilicon melt with the pressure (low vacuum) of 80 hPa or more for onehour or more to carry out the cristobalitizing step and then perform thedissolving step with the pressure (high vacuum) of 70 hPa or less forone hour or more and nine hours or less.

It is to be noted that the cases where the increase in number ofrotations of the crucible, the increase in gas flow rate, or thereduction in furnace pressure was performed have been described above,but these increases or reduction can be combined and the dissolving stepcan be effected in the present invention. Further, as regards themagnetic field, the same intensity of the magnetic field does notnecessarily have to be used in the cristobalitizing step and thedissolving step.

It is to be noted that the present invention is not restricted to theforegoing embodiment. The foregoing embodiment is just an illustrativeexample, and any example that has substantially the same configurationand exercises the same functions and effects as the technical conceptdescribed in claims according to the present invention is included inthe technical scope of the present invention.

The invention claimed is:
 1. A method for manufacturing a silicon singlecrystal, the method comprising: a raw material melting step of meltingpolycrystalline silicon accommodated in a crucible to obtain a siliconmelt; and a pulling step of bringing a seed crystal into contact with amelt surface of the silicon melt and pulling up the seed crystal to growthe silicon single crystal, wherein, after the raw material melting stepand before the pulling step, there are performed: a cristobalitizingstep of leaving the silicon melt at a predetermined number of rotationsof the crucible with a predetermined gas flow rate and a predeterminedfurnace pressure to generate cristobalite on a surface of the cruciblewhile applying a magnetic field; and a dissolving step of partiallydissolving the cristobalite by carrying out any one of an increase innumber of rotations of the crucible, an increase in gas flow rate, and areduction in furnace pressure beyond counterpart figures in thecristobalitizing step, wherein the dissolving step is performed for onehour or more and nine hours or less.
 2. The method for manufacturing asilicon single crystal according to claim 1, wherein the same magneticfield as that in the cristobalitizing step is applied at the dissolvingstep.
 3. The method for manufacturing a silicon single crystal accordingto claim 1, wherein the number of rotations of the crucible is adjustedto 3 rpm or less at the cristobalitizing step.
 4. The method formanufacturing a silicon single crystal according to claim 2, wherein thenumber of rotations of the crucible is adjusted to 3 rpm or less at thecristobalitizing step.
 5. The method for manufacturing a silicon singlecrystal according to claim 1, wherein the gas flow rate is adjusted to250 L/min or less at the cristobalitizing step.
 6. The method formanufacturing a silicon single crystal according to claim 2, wherein thegas flow rate is adjusted to 250 L/min or less at the cristobalitizingstep.
 7. The method for manufacturing a silicon single crystal accordingto claim 1, wherein the furnace pressure is adjusted to 80 hPa or moreat the cristobalitizing step.
 8. The method for manufacturing a siliconsingle crystal according to claim 2, wherein the furnace pressure isadjusted to 80 hPa or more at the cristobalitizing step.
 9. The methodfor manufacturing a silicon single crystal according to claim 1, whereinthe cristobalitizing step is performed for one hour or more.
 10. Themethod for manufacturing a silicon single crystal according to claim 2,wherein the cristobalitizing step is performed for one hour or more. 11.The method for manufacturing a silicon single crystal according to claim1, wherein the number of rotations of the crucible is increased to 5 rpmor more at the dissolving step.
 12. The method for manufacturing asilicon single crystal according to claim 2, wherein the number ofrotations of the crucible is increased to 5 rpm or more at thedissolving step.
 13. The method for manufacturing a silicon singlecrystal according to claim 1, wherein the gas flow rate is increased to300 L/min or more at the dissolving step.
 14. The method formanufacturing a silicon single crystal according to claim 2, wherein thegas flow rate is increased to 300 L/min or more at the dissolving step.15. The method for manufacturing a silicon single crystal according toclaim 1, wherein the furnace pressure is reduced to 70 hPa or less atthe dissolving step.
 16. The method for manufacturing a silicon singlecrystal according to claim 2, wherein the furnace pressure is reduced to70 hPa or less at the dissolving step.
 17. The method for manufacturinga silicon single crystal according to claim 1, wherein the magneticfield to be applied is a horizontal magnetic field and intensity of acenter magnetic field thereof is set to 3000 gausses or more and 5000gausses or less at the cristobalitizing step, the dissolving step, orboth the cristobalitizing step and the dissolving step.
 18. The methodfor manufacturing a silicon single crystal according to claim 2, whereinthe magnetic field to be applied is a horizontal magnetic field andintensity of a center magnetic field thereof is set to 3000 gausses ormore and 5000 gausses or less at the cristobalitizing step, thedissolving step, or both the cristobalitizing step and the dissolvingstep.